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        <li class="toc-entry toc-h3"><a href="#structural-markup">结构标记</a></li>
        <li class="toc-entry toc-h3"><a href="#interactive-components">互动组件</a></li>
        <li class="toc-entry toc-h3"><a href="#color-contrast">颜色对比</a></li>
        <li class="toc-entry toc-h3"><a href="#visually-hidden-content">视觉隐藏内容</a></li>
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<main class="col-12 col-md-9 col-xl-8 py-md-3 pl-md-5 bd-content" role="main">
  <h1 class="bd-title" id="content">无障碍浏览</h1>
  <p class="bd-lead">Bootstrap对创建可友好访问内容的功能和限制的简要概述。</p>
  <p>Bootstrap提供了一个易于使用的现成样式框架、布局工具和交互式组件框架，允许开发人员创建视觉上吸引人，功能丰富的开箱即用的网站和应用程序，实现易用性辅助增强的无障碍浏览平台。</p>
   
  <h2 id="overview-and-limitations">概述和限制</h2>
  <p>使用Bootstrap构建的任何项目的整体可访问性在很大程度上取决于作者的标记、额外的样式和脚本。但是，如果已经正确实现了这些功能，则完全可以使用Bootstrap创建实现<a href="https://www.w3.org/TR/WCAG20/"><abbr title="Web Content Accessibility Guidelines">Web内容无障碍指南WCAG</abbr> 2.0</a> (A/AA/AAA)、<a href="https://www.section508.gov/">Section 508</a>，第508节和类似的可友好访问性标准和要求的网站和应用程序。</p>
  <h3 id="structural-markup">结构标记</h3>
  <p>Bootstrap的造型和布局可以应用于各种标记结构。本文档旨在为开发人员提供最佳实践示例，以演示使用Bootstrap本身并说明适当的语义标记，包括可以解决潜在的可访问性问题的方法。</p>
  <h3 id="interactive-components">互动组件</h3>
  <p>Bootstrap的交互式组件（如模态对话框，下拉菜单和自定义工具提示）设计用于触摸，鼠标和键盘用户。通过使用相关的 <a href="https://www.w3.org/WAI/intro/aria"><abbr title="Web Accessibility Initiative">WAI</abbr>-<abbr title="Accessible Rich Internet Applications">ARIA</abbr></a> 角色和属性，这些组件也应该使用辅助技术（如屏幕阅读器）可以理解和操作。</p>
  <p>由于Bootstrap的组件有意设计为相当通用，因此作者可能需要包含进一步的ARIA角色和属性以及JavaScript行为，以更准确地传达其组件的精确性质和功能（通常在文档中注明）。</p>
  <h3 id="color-contrast">颜色对比</h3>
  <p>目前构成Bootstrap默认调色板的大多数颜色 - 在整个框架中用于诸如按钮变化，警报变化，形式验证指示符之类的功能，导致颜色<em>对比度不足</em>（低于推荐的<a href="https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html">WCAG 2.0色对比度为4.5：1</a>）光背景。作者将需要手动修改/扩展这些默认颜色以确保足够的色彩对比度。</p>
  <h3 id="visually-hidden-content">视觉隐藏内容</h3>
  <p>支持视觉隐藏的内容、但保持可访问的辅助技术，如屏幕阅读器，可以使用<code class="highlighter-rouge">.sr-only</code>类风格。在需要向非视觉用户传达额外的视觉信息或提示（例如通过使用颜色表示的含义）的情况下，这通常很有用。</p>
  <figure class="highlight">
    <pre><code class="language-html" data-lang="html"><span class="nt">&lt;p</span> <span class="na">class=</span><span class="s">"text-danger"</span><span class="nt">&gt;</span>
  <span class="nt">&lt;span</span> <span class="na">class=</span><span class="s">"sr-only"</span><span class="nt">&gt;</span>Danger: <span class="nt">&lt;/span&gt;</span>
  This action is not reversible
<span class="nt">&lt;/p&gt;</span></code></pre>
  </figure>
  <p>对于视觉隐藏的交互式控件，例如传统的“skip”跳过链接，<code class="highlighter-rouge">.sr-only</code>与<code class="highlighter-rouge">.sr-only-focusable</code>命令组合使用，这将确保一旦聚焦（对于瞄准的键盘用户）控件变得可见。</p>
  <figure class="highlight">
    <pre><code class="language-html" data-lang="html"><span class="nt">&lt;a</span> <span class="na">class=</span><span class="s">"sr-only sr-only-focusable"</span> <span class="na">href=</span><span class="s">"#content"</span><span class="nt">&gt;</span>Skip to main content<span class="nt">&lt;/a&gt;</span></code></pre>
  </figure>
  <h3 id="reduced-motion"><span class="bd-content-title">减少动作</span></h3>

  <p>Bootstrap包括对首选减少<a href="https://drafts.csswg.org/mediaqueries-5/#prefers-reduced-motion"><code class="highlighter-rouge">prefers-reduced-motion</code>媒体功能的支持.</a>.在允许用户指定减少运动的首选项的浏览器/环境中，Bootstrap中的大多数CSS过渡效果（例如，打开或关闭模式对话框时，或轮播中的滑动动画）将被禁用.</p>
  <h2 id="additional-resources">扩展资源</h2>
  <ul>
    <li><a href="https://www.w3.org/TR/WCAG20/">Web Content Accessibility Guidelines 《WCAG) 2.0(Web内容辅助功能指南（WCAG）2.0》</a></li>
    <li><a href="http://a11yproject.com/">The A11Y Project</a></li>
    <li><a href="https://developer.mozilla.org/en-US/docs/Web/Accessibility">MDN accessibility documentation《MDN辅助功能文档》</a></li>
    <li><a href="https://tenon.io/">Tenon.io Accessibility Checker《Tenon.io辅助功能检查器》</a></li>
    <li><a href="https://developer.paciellogroup.com/resources/contrastanalyser/">Colour Contrast Analyser (CCA)《彩色对比分析仪（CCA）》</a></li>
    <li><a href="https://github.com/squizlabs/HTML_CodeSniffer">“HTML Codesniffer” bookmarklet for identifying accessibility issues《用于识别辅助功能问题的“HTML代码转换”书签》</a></li>
  </ul>
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